Plastic closure cap with early venting inner seal

Abstract

The invention concerns a plastic screwable closure cap which possesses a bung type internal seal (4) for sealing a closeable container. The internal seal comprises a narrow sealing portion with an insert portion (6) immediately beneath, said insert portion serving to centre and gently introduce the internal seal. In order to attain the earliest possible venting of the closure cap when screwing off, venting recesses are provided on the insert zone (6). These prevent the insert portion from sealing the container, and enable the release of gas from the container as soon as the sealing portion comes out of engagement with the container mouth. The side surfaces of the vent recesses also serves as friction surfaces, in order to generally flatten irregularities on the container mouth before the actual sealing portion is engaged.

We claim: 
     
       1. A screwably plastic closure cap for sealing a container at its orifice, said closure cap comprising: a cylindrical cap wall;   a cap base having an inner surface and being adjacent to said cylindrical cap wall;   an internal seal extending downwardly from the inner surface of said cap base, said internal seal possessing a radially outer surface comprising a surrounding sealing portion on its outer edge for internal sealing of the container orifice to be closed and possessing an insert portion beneath the sealing portion;   said sealing portion being spaced from the cap base and defining a maximum outer diameter of the internal seal prior to placement on the container;   said insert portion comprising a compression zone, whereby the compression zone is designed to engage the container orifice and be compressed when the insert portion is inserted into the orifice;   wherein the radially outer surface of the internal seal possesses, in the area of said insert portion, at least one vent recess, said vent recess extending at least over the entire height of the compression zone, said compression zone and said at least one vent recess being axially below said sealing portion.   
     
     
       2. A closure cap according to claim 1, characterized in that the outer diameter of the internal seal, in the area of the insert portion (6), reduces towards the lower end (7) of said internal seal. 
     
     
       3. A closure cap according to claim 1, characterized in that the width (11) of the vent recess does not exceed 1/15 of the circumference of the internal seal. 
     
     
       4. A closure cap according to claim 1, characterized in that, on the front end (18) of the vent recess seen in the direction of screwing on (17), the surface of said vent recess meets the uninterrupted surface formed on the insert portion as a face (16), along an effective cutting edge (18) and approximately at a right angle. 
     
     
       5. A closure cap according to claim 1, characterized in that a plurality of vent recesses (9) are arranged to be distributed around the circumference of the internal seal. 
     
     
       6. A closure cap according to claim 5, characterized in that, between the vent recesses, cutting edges are provided to flatten irregular or damaged edges of the mouth of plastic containers. 
     
     
       7. A closure cap according to claim 6, characterized in that the vent recesses are arranged at a uniform distance from one other. 
     
     
       8. A closure cap according to claim 7, characterized in that the vent recesses (9) are immediately adjacent to one another. 
     
     
       9. A closure cap according to claim 8, characterized in that, at the rear end (19) of the vent recess (9) seen in the direction of screwing on (17), the surface of the vent recess meets an uninterrupted surface of the insert portion at a shallow angle as a heel (21). 
     
     
       10. A closure cap according to claim 1, characterized in that the internal seal possesses at least 25, and at the most 50, vent recesses (9). 
     
     
       11. A closure cap according to claim 1, characterized in that the insert portion possesses a slipping zone in its lower most region, the diameter within that slipping zone reducing towards the lower end, and the outer diameter between the slipping zone and the sealing portion possessing a local minimum value so that the local maximum diameter will arise at the upper end of said slipping zone, said maximum diameter being designed to engage the container at the orifice when said closure cap is applied to the container.